Avila says police received an anonymous tip that led them to the apartment, which is about 5 miles (8 kilometers) from the Walmart store where the shooting took place late Wednesday.

Thornton Police didn't reveal any details spontaneously neither about the circumstances of the shooting nor the people who were responsible for the shooting.

As a matter of precaution, the public should be cautious until the suspect is taken into custody.

"We had to discern what exactly was going on, whether that was a suspect or a citizen wondering what was going on and concerned by the sound of gunshots", Avila said. However, a Thornton PD spokesperson did refer to the shooting as a heinous act.

Police said they have yet to establish a motive for the rampage and that Ostrem had only "a minimal criminal history".

He said at this point, customers started screaming and running for the exits.

"It took a while because it was so many people, it was mass chaos in there", Avila said. The victims were in the same area of the store, but it is unclear if they knew each other.

"I was scared", Stephens said.

Court records also show Ostrem filed for Chapter 7 bankruptcy in 2015.

Authorities are asking anyone with information about the shooting to contact police at 720-977-5069 or Metro Denver Crime Stoppers at 720-913-7867. My goal in life is to one day write a Batman screenplay.

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